Angiolymphoid hyperplasia with eosinophilia (ALHE) is commonly regarded an angioproliferative process characterized by the presence of prominent, bizarrely shaped blood vessels. These vessels are accompanied by an inflammatory infiltrate that is thought to be a reactive component. Both the cell of origin and the pathogenesis of ALHE remain controversial. To define the histogenesis of this disorder, we analyzed the phenotypic and genotypic profile of the inflammatory infiltrate in ALHE by immunohistochemistry and T-cell receptor gene rearrangement by polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis, as well as automated high-resolution PCR fragment analysis. Five of 7 ALHE patients displayed a clonal T-cell population and proliferative T-cell activity in lesional tissue. Most of these cases followed a protracted and therapy-reluctant course with recurrences. These data suggest that ALHE or a subset of ALHE cases harboring a clonal T-cell population may represent a T-cell lymphoproliferative disorder of a benign or low-grade malignant nature.